Such optoelectronic apparatuses, having a transmission element, a receiving element and, on occasion, a translucent, plastic body are used, for example, for digital and/or analog signal transmission between two electrical current circuits galvanically isolated from one another.
In industrial measurements technology, especially in automation, and process control, technology, such optoelectronic apparatuses are applied and required in field devices for galvanic isolation of the electrical current circuits for explosion protection. Such field devices ascertain, for example, pressure, flow, fill level, dielectric constant, surface or interface, temperature or some other physical and/or chemical process quantity as the process variable in the conducting of a process. Available from the assignee are, for example, field devices under the marks, CERABAR, DELTABAR, DELTAPILOT, PROMASS, LEVELFLEX, MICROPILOT, PROSONIC, SOLIPHANT, LIQUIPHANT, EASYTEMP, which serve primarily to determine and/or to monitor at least one of the above referenced process variables of a medium in a container.
The galvanic isolation is applied both in the case of so-called two conductor devices, which transmit both the power supply energy and the measurement signal via a single line-pair, as well as also in the case of four conductor devices, which use separate line-pairs, one for transmitting the measuring signal and the other for transmitting the power supply energy. Examples of such field devices using optocouplers for galvanically isolated electrical current circuits are described in U.S. Pat. No. 4,654,771A and WO 2004/048905 A1.
Optoelectronic apparatuses using optocouplers are described, for example, in DE 199 20 403 A1 and U.S. Pat. No. 6,947,620 B2. In general, such optoelectronic apparatuses are composed of at least one transmission element, e.g. a light emitting diode, and at least one receiving element, e.g. a photodiode or a phototransistor, which are spatially and galvanically isolated from one another via at least one light conducting element.
In order that such optoelectronic apparatuses used for the signal transmission can satisfy the explosion protection required in industrial measurements and automation technology, also required are minimum separations between galvanically isolated, electrical current carrying components, as well as minimum values for air distances, insulation thicknesses and electrical current creep paths. Thus, for example, in the case of a maximum allowable voltage of 250 V, the air distances and the creep path length between galvanically isolated electrical current circuits must be at least 10 mm, or the thickness of solid insulation at least 1 mm. These separations refer, in such case, especially, to the minimum distances between the operationally electrical current carrying connections and conductive traces of the electrical current circuits coupled by means of such optoelectronic apparatuses. Furthermore, there are, for such apparatuses serving as optocouplers, increased requirements also as regards temperature resistance and explosion endangerment risk, as well as also as regards damage scenarios accompanying possibly occurring cases of overloading.
In order, in spite of the high safety requirements, to enable an, as much as possible, high coupling factor, as well as an, as much as possible, compact form of construction of such optoelectronic apparatuses, their light conducting elements are correspondingly embodied to meet the requirements of explosion protection and signal transmission.